U.S. patent application number 11/976044 was filed with the patent office on 2008-05-15 for driver and driving method for solid-state imaging device.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Yoshiyuki Tomizawa, Toshiaki Utsumi.
Application Number | 20080111898 11/976044 |
Document ID | / |
Family ID | 39368826 |
Filed Date | 2008-05-15 |
United States Patent
Application |
20080111898 |
Kind Code |
A1 |
Tomizawa; Yoshiyuki ; et
al. |
May 15, 2008 |
Driver and driving method for solid-state imaging device
Abstract
According to one embodiment the amount of noise in the OB
interval of a video signal when an electron-multiplying solid-state
imaging device is driven with each of predetermined multiplication
gains has been measured and stored in advance. The amount of noise
in the OB interval of a video signal when the solid-state imaging
device is driven with a drive voltage of a predetermined magnitude
is measured. The magnitude of the drive voltage is corrected on the
basis of the measured amount of noise and the stored amount of
noise corresponding to one of the predetermined multiplication
gains.
Inventors: |
Tomizawa; Yoshiyuki;
(Yokohama-shi, JP) ; Utsumi; Toshiaki;
(Akishima-shi, JP) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
39368826 |
Appl. No.: |
11/976044 |
Filed: |
October 19, 2007 |
Current U.S.
Class: |
348/231.99 ;
348/294; 348/E3.022; 348/E5.031; 348/E5.079; 348/E5.091 |
Current CPC
Class: |
H04N 5/37213 20130101;
H04N 5/361 20130101 |
Class at
Publication: |
348/231.99 ;
348/294; 348/E05.031; 348/E05.091 |
International
Class: |
H04N 5/76 20060101
H04N005/76; H04N 5/335 20060101 H04N005/335 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 10, 2006 |
JP |
2006-305504 |
Claims
1. A driver for a solid-state imaging device comprising: a
generating unit configured to generate a drive voltage having a
magnitude to obtain a predetermined multiplication gain to an
electron-multiplying solid-state imaging device; a producing unit
configured to produce a video signal on the basis of an output
signal of the solid-state imaging device which is driven with a
drive voltage output from the generating unit; a storage unit
configured to store the amount of noise in the OB (optical black)
interval of a video signal obtained from the producing unit when
the solid-state imaging device is driven with each of a plurality
of predetermined multiplication gains; a measurement unit
configured to measure the amount of noise in the OB interval of a
video signal obtained from the producing unit when the solid-state
imaging device is driven with a drive voltage corresponding to one
of the predetermined multiplication gains; and a correction unit
configured to correct the magnitude of the drive voltage output
from the generating unit on the basis of the amount of noise
measured by the measuring unit and the amount of noise stored in
the storage unit and corresponding to the one of the predetermined
multiplication gains.
2. The driver according to claim 1, wherein the correction unit
corrects the magnitude of the drive voltage output from the
generating unit so that the amount of noise measured by the
measuring unit coincides with the amount of noise stored in the
storage unit and corresponding to the one of the predetermined
multiplication gains.
3. The driver according to claim 1, wherein the amount of noise is
expressed in terms of a peak-to-peak amplitude value obtained in
the OB interval of the video signal output from the producing
unit.
4. The driver according to claim 3, wherein the correction unit
corrects the magnitude of the drive voltage output from the
generating unit so that the peak-to-peak amplitude value measured
by the measuring unit coincides with the peak-to-peak amplitude
value stored in the storage unit and corresponding to the one of
the predetermined multiplication gains.
5. The driver according to claim 3, wherein the correction unit
makes a comparison between the peak-to-peak amplitude value
measured by the measuring unit and the peak-to-peak amplitude value
stored in the storage unit and corresponding to the one of the
predetermined multiplication gains and, when the former
peak-to-peak amplitude value is lower than the latter, corrects the
magnitude of the drive voltage output from the generating unit so
that the former becomes equal to the latter.
6. A color camera equipped with an electron-multiplying solid-state
imaging device comprising: a generating unit configured to generate
a drive voltage having a magnitude to obtain a predetermined
multiplication gain to the solid-state imaging device; a producing
unit configured to produce a video signal on the basis of an output
signal of the solid-state imaging device which is driven with a
drive voltage output from the generating unit; a processing unit
configured to perform predetermined signal processing on the video
signal output from the producing unit; a storage unit configured to
store the amount of noise in the optical black (OB) interval of a
video signal output from the producing unit when the solid-state
imaging device is driven with each of a plurality of predetermined
multiplication gains; a measurement unit configured to measure the
amount of noise in the OB interval of a video signal output from
the producing unit when the solid-state imaging device is driven
with a drive voltage corresponding to one of the predetermined
multiplication gains; and a correction unit configured to correct
the magnitude of the drive voltage output from the generating unit
on the basis of the amount of noise measured by the measuring unit
and the amount of noise stored in the storage unit and
corresponding to the one of the predetermined multiplication
gains.
7. For use with a color camera equipped with an
electron-multiplying solid-state imaging device, a drive voltage
generating unit configured to supply the solid-state imaging device
with a drive voltage having a magnitude to obtain a predetermined
multiplication gain, and a video signal producing unit configured
to produce a video signal on the basis of an output signal of the
solid-state imaging device driven with the drive voltage output
from the generating unit, a method of driving the solid-stage
imaging device comprising: storing the amount of noise in the
optical black (OB) interval of a video signal output from the
producing unit when the solid-state imaging device is driven with
each of a plurality of predetermined multiplication gains;
measuring the amount of noise in the OB interval of a video signal
output from the producing unit when the solid-state imaging device
is driven with a drive voltage corresponding to one of the
predetermined multiplication gains; and correcting the magnitude of
the drive voltage output from the generating unit on the basis of
the amount of noise measured by the measuring unit and the amount
of noise stored in the storage unit and corresponding to the one of
the predetermined multiplication gains.
8. The method according to claim 7, wherein the magnitude of the
drive voltage output from the generating unit is corrected so that
the measured amount of noise coincides with the stored amount of
noise corresponding to the one of the predetermined multiplication
gains.
9. The method according to claim 7, wherein the amount of noise is
expressed in terms of a peak-to-peak amplitude value obtained in
the OB interval of the video signal output from the producing
unit.
10. The method according to claim 9, wherein the magnitude of the
drive voltage output from the generating unit is corrected so that
the measured peak-to-peak amplitude value coincides with the stored
peak-to-peak amplitude value corresponding to the one of the
predetermined multiplication gains.
11. The method according to claim 9, wherein the magnitude of the
drive voltage is corrected by making a comparison between the
measured peak-to-peak amplitude value and the stored peak-to-peak
amplitude value corresponding to the one of the predetermined
multiplication gains and, when the former peak-to-peak amplitude
value is lower than the latter, correcting the magnitude of the
drive voltage output from the generating unit so that the former
becomes equal to the latter.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2006-305504, filed
Nov. 10, 2006, the entire contents of which are incorporated herein
by reference.
BACKGROUND
[0002] 1. Field
[0003] One embodiment of the invention relates to a driver and
driving method for an electron-multiplying solid-state imaging
device.
[0004] 2. Description of the Related Art
[0005] As is well known, an electron-multiplying solid-state
imaging device is capable of varying its multiplication gain
according to the magnitude of a drive voltage applied to its
multiplication section. With such an electron-multiplying
solid-state imaging device, the multiplication gain may gradually
decrease with time or according to the conditions under which it is
actually used even if the magnitude of a drive voltage applied to
it remains unchanged.
[0006] It is presently considered that the occurrence of gain
variations results from electrons which should increase in number
through electron multiplication ceasing to increase with time or
according to the conditions under which the imaging device is
actually used. For this reason, with an electron-multiplying
solid-state imaging device which has long been used, even when it
is supplied with a drive voltage of the same magnitude as at the
early time of use, it becomes impossible to attain the same
amplification gain as at that time.
[0007] JP-A 2003-347317 (KOKAI) discloses the configuration of a
charge multiplying device (CMD) and a CMD-mounting charge coupled
device (CCD) layer which allow the charge multiplication factor to
be arbitrarily adjusted by adjusting the cycle and the number of
times of a drive voltage of the first phase to perform charge
multiplication through impact ionization in comparison with
multi-phase drive voltages.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0008] A general architecture that implements the various feature
of the invention will now be described with reference to the
drawings. The drawings and the associated descriptions are provided
to illustrate embodiments of the invention and not to limit the
scope of the invention.
[0009] FIG. 1 is a diagram for use in explanation of a monitor
camera according to an embodiment of the present invention;
[0010] FIG. 2 is a block diagram of the signal processing system of
a color camera used in the monitor camera of the embodiment;
[0011] FIG. 3 is a characteristic diagram for use in explanation of
gain variations with time of the electron-multiplying CCD used in
the color camera of the embodiment;
[0012] FIG. 4 is a characteristic diagram for use in explanation of
gain variations of the electron-multiplying CCD used in the color
camera of the embodiment when different multiplication gains are
set in the CCD;
[0013] FIG. 5 is a characteristic diagram for use in explanation of
gain variations of the electron-multiplying CCD used in the color
camera of the embodiment when the CCD has different saturated
areas;
[0014] FIGS. 6A to 6C are diagrams for use in explanation of the
measurement of the amount of noise in the optical black (OB)
interval of a digital video signal which is made by the control
unit used in the color camera of the embodiment; and
[0015] FIG. 7 is a flowchart illustrating the gain variation
compensation processing performed by the control unit used in the
color camera of the embodiment.
DETAILED DESCRIPTION
[0016] Various embodiments according to the invention will be
described hereinafter with reference to the accompanying drawings.
In general, according to one embodiment of the invention, the
amount of noise in the OB interval of a video signal when an
electron-multiplying solid-state imaging device is driven with each
of predetermined multiplication gains has been measured and stored
in advance. The amount of noise in the OB interval of a video
signal when the solid-state imaging device is driven with a drive
voltage of a predetermined magnitude is measured. The magnitude of
the drive voltage is corrected on the basis of the measured amount
of noise and the stored amount of noise corresponding to one of the
predetermined multiplication gains.
[0017] FIG. 1 schematically shows a monitoring camera 11 which will
be described in this embodiment. The monitoring camera 11 is
mounted, for example, on the ceiling 12 of a building with a
mounting plate 13. The mounting plate 13 is fitted with a
supporting plate 14, which is fitted at its center with a rotating
plate 15.
[0018] The rotating plate 15 is fitted with a pair of supports 16
(only one is illustrated in FIG. 1) with its center of rotation
interposed therebetween, the supports extending downward in the
drawing. A color camera 17, which is virtually formed in the shape
of a globe, is rotatably mounted between the paired supports 16. In
this case, the color camera 17 has a lens 18 exposed in a portion
of its globe-like casing.
[0019] With the color camera 17 thus mounted, its lens 18 can be
moved in the pan direction by rotating the rotating plate 15 and in
the tilt direction by rotating the camera itself. In this case, the
rotating plate 15 and the color camera 17 are rotated by a pan
motor and a tilt motor, respectively, which are not shown in FIG.
1.
[0020] The color camera 17 is covered with a transparent cover 19.
The cover 19 has its one end portion formed in the shape of a
semi-globe in correspondence with the shape of the color camera 17
and its other end portion formed in the shape of an open cylinder.
The cover 19 covers the color camera 17 in such a way that the
camera is housed in it and its open end is attached to the
periphery of the supporting plate 14.
[0021] FIG. 2 shows the signal processing system of the color
camera 17. An incoming optical image of a subject produced by the
lens 18 is captured on an electron-multiplying CCD 20 and then
converted into an electrical signal corresponding to that optical
image. The electrical signal output from the CCD 20 undergoes noise
reduction and digitization processing in a correlated double
sampling/analog-to-digital conversion (CDS/ADC) unit 21. The
resulting digital video signal is then applied to a video
processing unit 22 where it undergoes predetermined video signal
processing.
[0022] In the video processing unit 22, the input digital video
signal undergoes video signal processing, such as sharpness
processing, contrast processing, gamma correction processing, white
balance processing, white pixel compensation processing,
compression processing, etc. The video signal output from the video
processing unit 22 is converted into analog form by a
digital-to-analog conversion (DAC) unit 23 and then applied through
an output terminal 24 to an external monitor 25 for visual
display.
[0023] All the operations of the color camera 17 including the
above image capture operation are controlled by a control unit 26.
The control unit 26 has a central processing unit (CPU) 26a built
in and responds to control information from a personal computer
(PC) 33 to be described later to control each component so that the
contents of control are reflected.
[0024] In this case, the control unit 26 employs a memory unit 26b.
The memory unit 26b includes a read-only memory (ROM) containing a
control program to be executed by the CPU 26a, a random access
memory (RAM) which provides the CPU 26a with a working area, and a
nonvolatile memory containing various items of configuration and
control information.
[0025] In addition, the control unit 26 is adapted to drive the
aforementioned pan motor 28 through a driver 27. In this case, the
control unit 26 is able to control the direction and speed of
rotation of the pan motor 27. Furthermore, the control unit 26 is
adapted to drive the aforesaid tilt motor 30 through a driver 29.
In this case, the control unit 26 is able to control the direction
and speed of rotation of the tilt motor 30.
[0026] The control unit 26 is connected through a communication
interface (I/F) 31 and an input/output terminal 32 to the PC 33.
Thereby, the control unit 26 is allowed to send a digital video
signal which has been processed by the video processing unit 22 to
the PC 33 for visual display on it as well as to control each
component on the basis of control information supplied from the PC
33.
[0027] The control unit 36 controls a drive unit 34 for driving the
CCD 20. The drive unit 34 drives the CCD 20 with a multiplication
gain corresponding to the magnitude of a drive voltage VDRV output
from a drive voltage generating unit 35. The control unit 26
controls the magnitude of the drive voltage VDRV output from the
drive voltage generating unit 35 so that the multiplication gain
required by the PC 33 is attained.
[0028] In view of gain variations of the CCD 20 which occur with
time or according to the conditions where the camera is actually
used, the control unit 26 is equipped with a noise amount
measurement unit 26c and a correction unit 26d to correct the
magnitude of the drive voltage VDRV from the drive voltage
generating unit 35 so that the multiplication gain required by the
user is correctly attained at all times even if gain variations
occur.
[0029] That is, with the electron-multiplying CCD 20, it is known
that gain variations occur, i.e., its multiplication gain gradually
decreases with time or according to the conditions where it is
actually used even if the magnitude of the applied drive voltage
VDRV remains unchanged. In this case, as the conditions where the
camera is actually used, the required multiplication gain and the
number of pixels which are in the saturated state (the saturated
area) significantly affect the gain variations.
[0030] FIG. 3 shows a measurement illustrating the relationship
between the magnitude of the drive voltage VDRV required to attain
a constant multiplication gain and the time. It can be seen that
the same gain cannot be attained unless the magnitude of the drive
voltage VDRV is increased with time.
[0031] FIG. 4 shows a measurement in which, with three
multiplication gains set by drive voltages A, B and C
(A<B<C), the change in each of the multiplication gains with
time is expressed in terms of the change in drive voltage required
to maintain the corresponding set gain. It can be seen that the
higher the multiplication gain, i.e., the higher the drive voltage,
the greater the change in gain becomes.
[0032] FIG. 5 shows a measurement in which, when the saturated area
makes up 100%, 50% and 10% of the total pixels of the CCD 20, the
change in multiplication gain with time is expressed in terms of
the change in drive voltage required to maintain the same gain. It
can be seen that the larger the saturated area, the greater the
change in gain becomes.
[0033] In this embodiment, when the color camera 17 is first
requested to capture an image with a predetermined multiplication
gain (for example, 1,000, 500, 250, . . . ), the control unit 26
causes the drive voltage generating unit 35 to generate a drive
voltage VDRV of a previously set magnitude corresponding to that
multiplication gain and apply it to the CCD 20. At this point, the
control unit 26 measures, through its noise measuring unit 26c, the
amount of noise in the optical black (OB) interval of a digital
video signal actually obtained from the CDS/ADC unit 21.
[0034] On the other hand, the multiplication gain varies from CCD
to CCD even if the same drive voltage is applied. In the camera
factory, therefore, gain matching is performed at the stage of
adjustment in such a way that the magnitudes of drive voltages
required to attain specified multiplication gains (for example,
1,000, 500, 250, . . . ) of the CCD 20 are set for each color
camera.
[0035] In the factory, at the stage of adjusting the multiplication
gains, the amount of noise in the OB interval of a digital video
signal actually obtained from the CDS/ADC unit 21 is measured for
each of the multiplication gains (for example, 1,000, 500, 250, . .
. ). The measured amounts of noise are then stored in the memory
unit 26b as reference values.
[0036] The control unit 26 corrects the magnitude of a drive
voltage VDRD being generated from the drive voltage generating unit
35 in the correction unit 26d by comparing the current amount of
noise being measured by the noise measuring unit 26c with the noise
reference values stored in the memory unit 26b so that a currently
required multiplication gain is attained, namely, the current
amount of noise coincides with one of the reference values, thereby
compensating for a decrease in the multiplication gain of the CCD
20.
[0037] Assuming that the amount of noise in the OB interval of a
digital video signal when no electron multiplication is required
(electron multiplication is off) is N, the amount of noise in the
OB interval of the digital video signal when predetermined electron
multiplication is required (electron multiplication is on) is Nem,
and the multiplication gain is Gem, the following relation holds:
Nem.varies.Gem.times.N
[0038] That is to say, this embodiment employs the fact that
measuring Nem allows us to know the actual multiplication gain
Gem.
[0039] In short, the embodiment employs the fact that noise in the
OB interval within one horizontal scan period of a digital video
signal actually obtained from the CDS/ADC unit 21 as shown in FIG.
6A is also subjected to electron multiplication. The amount of
noise, N, in the OB interval when electron multiplication is off is
expressed in terms of the peak-to-peak amplitude value in the OB
interval as shown in FIG. 6B. The amount of noise, Nem, in the OB
interval when electron multiplication is on is expressed in terms
of the peak-to-peak amplitude value in the OB interval as shown in
FIG. 6C.
[0040] With the measurement of the amount of noise based on data in
only one horizontal scan period, the accuracy is poor due to the
influence of random noise. For this reason, measurements are made
over tens of horizontal scan periods to one vertical scan period
and the measurements are averaged, thereby enhancing the
accuracy.
[0041] FIG. 7 is a flowchart for the aforementioned multiplication
gain correction processing. That is, when the processing is started
(step S1) at the stage of multiplication gain adjustment at the
factory, the amount of noise in the OB interval of a digital video
signal from the CDS/ADC unit 21 is measured for each of the
multiplication gains (for example, 1,000, 500, 250, . . . ) and
then the measurements (N1000, N500, N250, . . . ) are stored in the
memory unit 26b as reference values (step S2).
[0042] After that, when electron multiplication is required at the
time of actual image capture, the control unit 26 drives the CCD 20
with a drive voltage VDRV of a preset magnitude corresponding to
the required multiplication gain (for example, 1,000) and measures
the amount of noise, N1000A (actual), in the OB interval of a
digital video signal from the CDS/ADC unit 21 (step S3).
[0043] The control unit 26 then makes a comparison between the
amount of noise, N1000A, in the OB interval of the digital video
signal and the amount of noise, N1000, stored in the memory unit
26b for the same multiplication gain (1,000) to decide whether or
not N1000A<N1000 (step S4).
[0044] If NO in step S4, then the control unit 26 decides that the
multiplication gain of the CCD 20 has not decreased and continues
to drive the CCD 20 with the aforesaid preset drive voltage VDRV
with the result that the procedure is complete (step S6).
[0045] If, on the other hand, YES in step S4, i.e.,
N1000A<N1000, then the control unit 26 decides that the
multiplication gain of the CCD 20 has decreased and then corrects
the multiplication gain so that N1000A becomes equal to N1000 (step
S5), thereby completing the procedure (step S6).
[0046] According to the embodiment described above, the amount of
noise, A, in the OB interval of a digital video signal actually
obtained when the CCD is driven by the drive voltage corresponding
to a required multiplication gain is compared with the amount of
noise, B, in the OB interval which has been stored in the memory
unit 26b as a reference value when the CCD was driven with that
multiplication gain and, when A<B, the multiplication gain is
corrected so that A=B. Even if gain variations occur with time or
according to the conditions in which the color camera is actually
used, therefore, it becomes possible to compensate for the gain
variations in real time, allowing the electron-multiplying CCD 20
to be driven at all times with a required multiplication gain.
[0047] While certain embodiments of the inventions have been
described, these embodiments have been presented by way of example
only, and are not intended to limit the scope of the inventions.
Indeed, the novel methods and systems described herein may be
embodied in a variety of other forms; furthermore, various
omissions, substitutions and changes in the form of the methods and
systems described herein may be made without departing from the
spirit of the inventions. The accompanying claims and their
equivalents are intended to cover such forms or modifications as
would fall within the scope and spirit of the inventions.
* * * * *